Propane or Pro-pain?

I'm keen to keep the LPG/Propane kit outside the van, the problem is that I have a refillable LPG bottle but not a chassis mount tank. I've been given a tiny 4 litre kit off a moped that is vapour take off (need this as most cars etc are liquid with a tube to the bottom of the tank like a trigger spray disinfectant bottle). 

The moped had done 4 miles from new factory fit LPG and was sold for £100 as it never worked properly, having found it's got a vapour multiport I'm not surprised!

Safety and risk assessment aside (you must satisfy yourself that any LPG work carried out is safe, certified and inspected by a qualified person), I plan to swap this multiport onto a larger tank, the issue is that I will be removing the plunger from the solenoid valve as it wants to draw an amp at 12v all the time the gas is on. I'll be sticking to the manual valve used on calor bottles etc, for decades.

Again all this must be safe, I'm very lucky as I have the help of a friend who is LPG certified and have a VERY good LPG parts shop locally.

Multi-valve...

Tank...

I should be able to get a vapour system for very little cost, I will need to get a frame made to bolt through the floor and this needs to be sorted with the waste and water tanks.